Safety system for an automatic gearbox

ABSTRACT

For an automatic gearbox (2) a safety system is proposed in which erroneous releasing of the clutch or brake during cross-over is detected by the fact that the time variations of the transmission input speed and of the product of the transmission output speed multiplied by the first reduction ratio do not increase.

The invention relates to a safety system for an automatic gearbox inwhich for an upshift or a downshift an error of the releasing clutch orbrake can be detected when the difference of the transmission inputspeed and the product of the transmission output speed multiplied by thefirst reduction ratio does not steadily increase.

BACKGROUND OF THE INVENTION

By the generic expression automatic gearbox is to be understoodelectrohydraulically controlled automatic gearboxs where the gearshiftis carried out as cross-over gearshift. In cross-over gearshifts, thegearshift results by a first clutch or brake releasing and second clutchor brake engaging. In automatic gearboxs, it is usual, in general, tomonitor the orderly operation thereof in order to prevent situationscritical to safety. Monitored are the input signals made available bythe sensors, the electromagnetic actuators, the electronic transmissioncontrol and, via acknowledged variables, the clutches and brakes thattake part in the gearshift. It is of special interest here to detect afaulty releasing of a clutch or brake since this can result in theblocking of the transmission and subsequent destruction. A faultyrelease is thus extremely critical to safety.

SUMMARY OF THE INVENTION

Therefore, the invention intends to solve the problem of providing, foran automatic gearbox, a safety system which detects a faulty release ofa clutch or brake.

According to the invention, the solution of the problem is that at thestart of a gearshift, the electronic control device cyclicallycalculates from the measured transmission output speed, as a firstparameter G1, the product of transmission output speed multiplied by thefirst ratio, and as second parameter G2 measures the transmission inputspeed. From the difference between the first and second parameters atime variation is determined for two consecutive values. The electroniccontrol device detects an error of the releasing clutch or brake whenthe the difference after load take-up does not increase. This solutionoffers the advantage that with the aid of the two parameters, it ispossible to assess whether the gearshift proceeds methodically. In caseof an error, the gearshift is discontinued and the automatic gearboxremains in the initial gear.

In one embodiment, it is proposed that the first and second parametersbe each surrounded by an envelope curve. An error exists when after theload take-up the envelope curves still overlap so that the values of thetwo parameters G1, G2 represent within the envelope curves the faultyarea and values and outside the envelope curves the fault-free area.This embodiment offers the advantage that tolerances of the speedsensors are not immediately assessed as an error of the releasing clutchor brake.

In another embodiment, it is proposed that briefly increased slip on theinput gears be detected when the values of the first parameter G1 arebelow the second parameter G2.

BRIEF DESCRIPTION OF THE DRAWING(S)

An embodiment is illustrated in the figures that show:

FIG. 1 is a system diagram of an automatic gearbox;

FIG. 2 is a clutch-brake logic of the automatic gearbox;

FIG. 3 is an ideal time variation of the first and second parameters foran upshift;

FIG. 4 is an ideal time variation of the first and second parameters fora downshift;

FIG. 5a is a faulty time variation for an upshift, 1st case;

FIG. 5b is a faulty time variation for an upshift, 2nd case; and

FIG. 6 is a diagram, number of the successful/unsuccessful testconditions.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In FIG. 1 is shown an automatic gearbox 2. The automatic gearbox 2 iscomprised of a hydrodynamic converter 7, a combined planetarytransmission 11 with differential 12, a hydraulic control device 4 and aelectronic control device 5. An internal combustion engine 1 drives theautomatic gearbox 2 via input shaft 6. An electronic engine controldevice 3 controls or regulates the internal combustion engine 1. Theinput shaft 6 is non-rotatably connected with the hydrodynamic converter7 and drives the impeller 8 thereof. It is known that the hydrodynamicconverter 7 consists of the impeller 8, one turbine wheel 9 and onestator 10. A converter bridge clutch, parallel to the hydrodynamicconverter 7, is shown without reference numeral. When the converterbridge clutch is actuated, the turbine shaft rotates at the same speedas the input shaft 6. The combined planetary transmission 11 consists oftwo planetary gear pairs and the clutches and brakes B to F. From FIG. 2can be seen the corresponding gear coordination for the clutch/brakecombination. The output takes place via the differential 12 and the twoaxle half shafts 13A and 13B. Since the mechanical part is not relevantfor a better understanding of the invention, no detailed description isgiven. The clutches and brakes B to F are controlled or regulated by theelectronic control device 5 via the hydraulic control device 4. Theelectromagnetic actuators and hydraulic successive sliders are in thehydraulic control device 4. The function blocks micro-controller 14,memory 15, function block calculation unit 17 and function block controlactuators 16 of the electronic control device 5 are shown in verysimplified form. The memory 15 is usually designed as EPROM or asbuffered RAM. In the memory 15 is stored the data relevant to thetransmission. The function block control actuator 16 serves to controlthe electromagnetic actuators in the hydraulic control device 4. Thefunction block calculation unit 17 serves to calculate the data relevantto the gearshift. The latter are determined from the input parameters 18to 21. Input parameters 20 are, for example, the signal of a selectorlever, the speed of the internal combustion engine, the signal of theposition of an accelerator pedal or throttle valve, the temperature ofthe hydraulic fluid, etc. The electronic engine control device 3 and theelectronic control device 5 are interconnected by a data line 21. Saiddata line 21 can be designed as a single-wire interface in order, forexample, to carry out an engine control. The data line 21, moreover, canalso be designed as bidirectional data line for a bus system such as CANbus. The transmission input speed 18 and the transmission output speedare additional input parameters for the control device 5.

FIG. 3 shows an ideal variation of both parameters G1 and G2 for anupshift. On the abscissa is plotted the time, on the ordinate areplotted the speed values of the first parameter G1 (G1=nAB×i1) and G2(G2=nT). Here nAB stands for the transmission output speed and nT forthe transmission input speed. For the three inquiry times t1, t2 and t3,there thus results for the first parameter G1 the series of points A, Band C. The series of points D, E and F results for the second parameterG2. The operation of the safety system is as follows: the gearshift isinitiated at the zero moment. As a first moment t1, the value of thefirst parameter G1, point A, is calculated and the value of the secondparameter G2, point D is determined. At a second moment t2, the firstparameter G1 is again calculated, point B, and the value of the secondparameter G2, point E, is determined. The time variation from first tosecond parameters is determined by the difference formation, whereforethe following applies:

    dG1=G1(t2)-G1(t1)

    dG2=G2(t2)-G2(t1)

At the third moment t3, the process is repeated and results in thepoints C and F. Between the moments t2 and t3, the second clutch tookover the load of the first clutch. Thereby changes the time variation ofthe second parameter G2. The calculated values of the first parameter G1remain almost constant, since the transmission output speed remainsalmost constant. The amount of the difference values of the first andsecond parameters are related to each other. For the inquiry moment t3,the deviation ratio is from point C to point F. In a methodicalvariation of the gearshift, the amount increases. In FIG. 3 areadditionally shown two hysteresis bands which surround the idealvariation of the first and second parameters. For the first parameterG1, the upper limit for the hysteresis band is marked with the referencenumeral 24 and the lower limit with the reference numeral 25. For thesecond parameter G2, the reference numeral 22 shows the upper limit andthe reference numeral 23 corresponds to the lower limit. The advantageobtained hereby is that measurement errors or interruptions in the speedsignals do not prevent the detection of an error. The band width of thehysteresis is obtained from tests and amounts, for example, to +/-100revolutions.

FIG. 4 shows an ideal variation of the two parameters G1 and G2 for adownshift. On the abscissa is plotted the time, on the ordinate areplotted the speed values of the first parameter G1 (G1=nAB×i1) andsecond parameter G2 (G2=nT). What has been said in relation to FIG. 3applies to the calculation of the two parameters and of the process.

FIG. 5A shows the variation of both parameters G1 and G2 for a faultyupshift. Unlike in a methodical upshift, the second parameter G2 is heredesignated with G2'. The envelope curves of both parameters remainoverlapped even after the load take-up. A first cause of error can bethat the releasing clutch or brake does not open methodically. A secondcause of error is when too low a pressure level exists in the engagingclutch. Because of this, the engaging clutch cannot take up the loadfrom the releasing clutch. The two causes of error produce a lesservariation of the second parameter G2' in comparison with the variationof the second parameter G2 during a methodical gearshift.

FIG. 5B shows another faulty upshift. The error becomes apparent in thatthe value of the first parameter G1, designated G1' here, is below thevalue of the second parameter G2. This is the case when sharp variablechanges in friction value, such as slippage, occur in the input gears ofthe vehicle.

FIG. 6 shows another embodiment. The point of departure here is that inthe time interval t2 to t3, the output and input speeds of thetransmission are detected with a higher inquiry frequency. As a resultof this, both parameters G1 and G2 are also calculated with a higherfrequency. During the time interval t2 to t3, the number of thesuccessful test conditions and of the unsuccessful test conditions iscounted and added up. A successful test condition exists when theenvelope curves of the first and second parameters do not overlap. InFIG. 6, the test condition in the time interval t2 to t2 (3) is negativeand in the time interval t2 (3) to t2 (5) the test conditions arepositive. In the time interval t2 (5) to t2 (8), the test condition, inturn, is not satisfied. At the moment t2 (8), the total exceeds a limitvalue. Starting from said limit value the gearshift is defined asmethodical.

REFERENCE NUMERALS

1 internal combustion engine

2 automatic gearbox

3 electronic engine control device

4 hydraulic control device

5 electronic control device

6 input shaft

7 hydrodynamic converter

8 impeller

9 turbine wheel

10 stator

11 combined planetary transmission

12 differential

13A axle half shafts

13B axle half shafts

14 micro-controller

15 memory

16 function block control actuators

17 function block calculation unit

18 transmission input speed

19 transmission output speed

20 input parameters

21 data line

22 hysteresis band

23 hysteresis band

24 hysteresis band

25 hysteresis band

G1 first parameter

G2 second parameter

G2' second parameter, faulty

G2" second parameter, faulty

I claim:
 1. A safety system for an automatic gearbox (2) comprisingclutches and brakes (B, F), a hydraulic control device (4) and anelectronic control device (5), which controls and regulates, via saidhydraulic control device (4), in accordance with input parameters (18 to21), said clutches and brakes (B, F) whereby a corresponding gear or aratio (i) is selected, said electronic control device (5) beingsupplied, as input parameters, transmission input speed (nT(t)),transmission output speed (nAB(t) and initiation of a shift, from afirst ratio (i1) to a second ratio (i2) carried out by release of afirst clutch or brake and engagement of a second clutch or brake, and,said electronic control device (5) calculates cyclically from themeasured transmission output speed (nAB(t)), as first parameter (G1),the product from the transmission output speed multiplied by the firstratio (G1=nAB×i1) and from the transmission input speed, as secondparameter (G2), from the first and second parameters (G1, G2), a timevariation is determined from two consecutive values by differenceformulation (dG1=G1(t2)-G1(t1) and dG2=G2(t2)-G2(t1), the time variationof said first and second parameters (G1, G2) each being betweenhysteresis curves (22, 23, 24 and 25), whereby said electronic controldevice (5) detects an error of the releasing clutch or brake when thehysteresis curves overlap after load take-up which represents a shiftfault.
 2. The safety system according to claim 1, wherein brieflyincreased slippage is detected on input gears of the transmission as aresult of the values of the first parameter (G1) being smaller than thevalues of the second parameter (G2).
 3. The safety system according toclaim 1, wherein for a predetermined time interval (t2) to (t3) afterload take-up, the transmission input speed (nT(t)) and the transmissionoutput speed (nAB(t)) are measured at a higher inquiry frequency, thefirst and second parameters (G1, G2) are determined therefrom and thenumber of the successful and unsuccessful test conditions is counted andadded together, an error being detected when the total does not exceed apresettable limit value, the successful test condition existing whenafter load take-up both envelope curves do not overlap and anunsuccessful test condition existing when both envelope curves dooverlap.